1. Field of the Invention
The invention pertains to apparatus for use in providing thin, substantially uniformly thick layers of material and, in particular, in connection with testing and study of microbiological cultures.
2. Description of the Prior Art
Testing and study of microbiological phenomena are, of course, extremely widespread and have applications in extremely varied fields of endeavor. Of increasing importance has been the application of microbiological techniques to testing of chemicals and environmental pollutants. It has been discovered that there is a very strong correlation between the tendency of a particular chemical to cause genetic mutations in bacteria ("mutagenicity") and the ability of such chemical to cause cancer ("carcinogenicity") in mammals and man. A particular application of this corporation is in the "Ames Salmonella/mammalian" microsome mutagencity test.
In the Ames test, test micro-organisms consist of bacteria mutated so that they are unable to synthesize histidine, an amino acid required for growth. The test bacteria are placed in a culture lacking histidine and including a chemical to be tested. If the chemical is not mutagenic, then the test bacteria will not be able to grow in the histidine-free culture; however, if there are mutagenic materials present, they will promote a reversal of the original mutation (which disabled the bacteria in the first place from synthesizing histidine); the test bacteria experiencing such a reversal (referred to as a reversion) will grow and form visible colonies. Thus, the appearance of colonies indicates that the chemical under test is mutagenic and probably carcinogenic as well. The degree of mutagenicity is determinable from the number of colonies produced by a given amount of the material under test.
Normally, the bacterial culture is continued in a vessel known as a petri dish comprising a covered container. The test compound contains besides the test material and the test bacteria a gelling agent. The mixture, in liquid form, is heated to melt the gelling agent and is then poured into the vessel, over a solid gelling agent, thus forming a thin film which solidifies upon cooling.
It is extremely desirable that the film containing the culture medium be of uniform thickness, which facilitates electronic counting of bacterial colonies, indicating the degree of mutagenicity. Inaccuracy results with such electronic counters if the thickness of the film in the culture medium is uneven in the petri dish. Also desirable is a capability of processing samples in batches as opposed to singly, thus facilitating efficiency.
In existing methods, spreading of the medium accomplished manually, with obvious drawbacks. Also, in existing methods and apparatus, processing of samples is usually on an individual as opposed to a batch basis. The device depicted and described in U.S. Pat. No. 3,310,292 issued Mar. 21, 1967, for "Serological Testing Device" utilizes vibration for agitating components in serological testing. Such device, however, does not function to equalize thickness of a layer of a compound and provides only for a limited number of items in a batch of samples to be processed simultaneously and requires individual lowering and lifting of slides used in connection with testing.
Thus, there has been a felt but unfulfilled need for apparatus for providing a thin, substantially uniformly thick layer of material, for testing and other purposes, and having the capability of conveniently processing a plurality of items simultaneously.